Originally Posted by Al_The_Man  If it were a non-isolated type and the correct steps were taken to confirm the connections, it is still possible to use it, it would just be that the secondary of the transformer would be referenced to ground.
Al. |
Yes but if you insert wall plug in wrong orientation (50% chance at least with european plug) then you get mains AC voltage as ground reference which would be
very dangerous.
To confirm if its isolated: disconnect all wires from it and measure ohms between primary and secondary windings. If it shows infinite ohms, it is isolating type.
Transformer info
http://www.allaboutcircuits.com/vol_2/chpt_9/5.html